There are many components, devices, equipment and systems required to make up an electrical power conversion and distribution system and many such power-electronics based systems have been developed and used in the prior art for numerous different applications, including motor controls. Usually a command is received either manually or automatically and one or more control objectives are achieved, regulated and maintained through sensing related controlled system parameters. Appropriate control decisions are typically made in a closed-loop or feed-forward fashion through a digital or analog controller to control power-electronics based switches such as SCRs, MOSFETs, IGBTs, Intelligent Power Modules, etc. For example, a power electronics based motor controllers typically include the following main subassemblies/functions:                Logic power supply;        Power electronics controller;        Control strategy/algorithm;        Power pass inverter (and rectifier if AC-DC-AC) devices/module;        Signal measurement (current, voltage temp, speed, etc.) and isolation;        Gate driver;        Power interconnect;        Logic interconnect;        Power sequencing, protection coordination and fault tolerance circuitry;        EMI and power quality filters for input and output;        Thermal management;        DC link capacitor;        Motor drive (DC Machine, Induction Machine, PMSM, wound field SM, SRM etc.); Controls I/O; and        Chassis.        
Although electrical power conversion and distribution systems have been developed, these power conversion technologies can not presently be effectively used for mission critical “more electric” future applications (e.g., land, sea, air transport) due to the harsh operating environments and conditions resulting in very low Mean Time Between Failure (MTBF) of the main components and very limited integrated protection coordination, diagnostics and monitoring to improve overall system health and reliability.
Much work has been directed toward improving the overall health and reliability of power control systems. In particular, U.S. Pat. No. 6,122,575 discloses a system, method, and computer program to assist a technician in troubleshooting an aircraft auxiliary power unit (APU). A portable computer is capable of downloading the fault data captured in a memory of the electric control unit (ECU). The fault data corresponds to one or more instances of APU failure. The computer is further programmed to compare the fault data to predetermined fault patterns stored in a database. Each record of the database has one of the fault patterns, a corresponding fault indication, and a corresponding service recommendation indication. The computer is further programmed so that when a record in which the fault pattern matches the fault data is found, the corresponding fault indication and service recommendation are retrieved from the database and provided to the technician via the computer's display or other suitable output mechanism.
Although the foregoing system provides enhanced information regarding service recommendations, the analysis is performed offline based only on past faults recorded. Therefore, this system does not provide any forward-looking analysis of potential failures or real time analysis of component health. Further, the system disclosed in U.S. Pat. No. 6,122,575 does not address component level critical devices, but only looks at the system at a subsystem level (e.g., APU). Furthermore, such a prior art health monitoring and diagnostics system does not address low MTBF and poor reliability of power-electronics based systems because the failure modes are not mitigated thoroughly, both at the system level and component level. Such conventional systems are not fault tolerant and due to limited Built-In-Tests (BIT) their proper operation can not be assessed at start-up or continuously monitored during normal or abnormal operation. Furthermore, lack of proper power sequencing, Soft-start, Soft-stop, ride-through, and proper protection against contingencies such as voltage-sag, voltage surge, system imbalance, under/over-frequency, over-load, over-temperature and wrong phase sequence conditions results in very stressful situations which usually degrade or cause total failure of major components of the system. Other limitations of prior art systems include the following:                Limited operation modes—e.g., only RUN and STOP modes available. The system is usually tripped (i.e., the load is disconnected from the power distribution system) under any abnormal condition without specifying the associated failure. As a result, a perceived faulty unit is commonly removed from the field and sent back to the supplier. After detailed testing and debugging in most cases, it is confirmed that the unit is capable of proper operation and consequently labeled as No Fault Found (NFF).        These nuisance trips and NFFs are labor intensive, tedious and not cost effective. User-friendly and efficient debugging of the system problems is not readily possible after a field trip/failure in a timely manner.        Power sequencing (initial turn-on or turn-off of the unit) is stressful and limited operation modes do not provide a mitigation opportunity for all the known system stressful transients or failure modes.        Lack of proper protection coordination, i.e., sequence, priority and timing control among different provisions of system and/or component level protection methods.        Detailed system level field operation or component level limitation data is usually not available at the design time.        All the failure modes or stressful periods of operation at the system or component level cannot be predicted at the time of design.        Stressful periods of operation or their actual cumulative effect cannot be monitored and accounted for in real-time to estimate the remaining time-to-failure.        Corrective maintenance cannot be reliably scheduled to replace degraded components to prevent components/system failure in the field during operation.        A major limitation still remains in relation to overall system reliability, and the fact that conventional diagnostic systems record fault data in formats that do not aid in diagnosing future failures of the monitored components.        